variog4
Computes Directional Variograms
Computes directional variograms for 4 directions provided by the user.
- Keywords
- spatial
Usage
variog4(geodata, coords = geodata$coords, data = geodata$data,
uvec = "default", breaks = "default", trend = "cte", lambda = 1,
option = c("bin", "cloud", "smooth"),
estimator.type = c("classical", "modulus"),
nugget.tolerance, max.dist, pairs.min = 2,
bin.cloud = FALSE, direction = c(0, pi/4, pi/2, 3*pi/4), tolerance = pi/8,
unit.angle = c("radians", "degrees"), messages, …)
Arguments
- geodata
a list containing element
coords
as described next. Typically an object of the class"geodata"
- a geoR data-set. If not provided the argumentscoords
must be provided instead.- coords
an \(n \times 2\) matrix containing coordinates of the \(n\) data locations in each row. Defaults to
geodata$coords
, if provided.- data
a vector or matrix with data values. If a matrix is provided, each column is regarded as one variable or realization. Defaults to
geodata$data
, if provided.- uvec
a vector with values to define the variogram binning. For further details see documentation for
variog
.- breaks
a vector with values to define the variogram binning. For further details see documentation for
variog
.- trend
specifies the mean part of the model. The options are:
"cte"
(constant mean),"1st"
(a first order polynomial on the coordinates),"2nd"
(a second order polynomial on the coordinates), or a formula of the type~X
whereX
is a matrix with the covariates (external trend). Defaults to"cte"
.- lambda
values of the Box-Cox transformation parameter. Defaults to \(1\) (no transformation). If another value is provided the variogram is computed after transforming the data. A case of particular interest is \(\lambda = 0\) which corresponds to log-transformation.
- option
defines the output type: the options
"bin"
returns values of binned variogram,"cloud"
returns the variogram cloud and"smooth"
returns the kernel smoothed variogram. Defaults to"bin"
.- estimator.type
"classical"
computes the classical method of moments estimator."modulus"
returns the variogram estimator suggested by Hawkins and Cressie (see Cressie, 1993, pg 75). Defaults to"classical"
.- nugget.tolerance
a numeric value. Points which are separated by a distance less than this value are considered co-located. Defaults to zero.
- max.dist
a numerical value defining the maximum distance for the variogram. Pairs of locations separated for distance larger than this value are ignored for the variogram calculation. Defaults to the maximum distance among the pairs of data locations.
- pairs.min
a integer number defining the minimum numbers of pairs for the bins. For
option = "bin"
, bins with number of pairs smaller than this value are ignored. Defaults toNULL
.- bin.cloud
logical. If
TRUE
andoption = "bin"
the cloud values for each class are included in the output. Defaults toFALSE
.- direction
a vector with values of 4 angles, indicating the directions for which the variograms will be computed. Default corresponds to
c(0, 45, 90, 135)
(degrees).- tolerance
numerical value for the tolerance angle, when computing directional variograms. The value must be in the interval \([0, 90]\) degrees. Defaults to \(\pi/8\).
- unit.angle
defines the unit for the specification of angles in the two previous arguments. Options are
"degrees"
and"radians"
.- messages
logical. Indicates whether status messages should be printed on the screen (or output device) while the function is running.
- …
arguments to be passed to the function
ksmooth
, ifoption = "smooth"
.
Value
The output is an object of the class variog4
,
a list with five components.
The first four elements are estimated variograms for the directions
provided and the last is the omnidirectional variogram.
Each individual component is an object of the class variogram
,
an output of the function variog
.
References
Further information on the package geoR can be found at: http://www.leg.ufpr.br/geoR.
See Also
variog
for variogram calculations and
plot.variog4
for plotting results
Examples
# NOT RUN {
var4 <- variog4(s100, max.dist=1)
plot(var4)
# }